Agitator and viscosimeter for sugar sirup or the like and apparatus utilizing the same

ABSTRACT

A viscosimeter which determines the viscosity of sirup in a batch vacuum crystallizer comprises an agitator including a rod which extends through a diaphragm overlying an opening in the crystallizer wall and is reciprocated, oscillated or wobbled by a drive combined with a detector which measures the force necessary to impart to the agitator a recurrent movement. The detector indicates the force on a viscosity scale and simultaneously actuates a device which records a viscosity curve. The viscosimeter forms part of an automatic control system which regulates the operation of the crystallizer.

United States Patent Thiele et al.

[ 1 Jan. 25, 1972 Henry Thiele; Tilo Von During; Gerd Wcgner, all of Wevelinghoven, Germany Inventors:

Assignee:

Filed: July 29, 1968 App1.No.: 748,366

Foreign Application Priority Data Nov. 23, 1967 Germany ..P 42701 US. Cl. ..73/59, 127/15 [56] References Cited Field oISearch ..l27/l5, 16;23/253 UNITED STATES PATENTS 2,668,442 2/1954 Osbourne ..73/59 7/1954 Boyle etal 2,696,735 12/1954 Woodward ..l ..73/59 3,l45,559 8/1964 Banks 3,403,546 10/1 968 Stratton ..73/54 FOREIGN PATENTS OR APPLICATIONS 171,191 4/1960 Sweden ..73/59 Primary ExaminerLouis R. Prince Assistant Examiner-Joseph W. Roskos AttorneyMichael S. Striker [57] ABSTRACT A viscosimeter which determines the viscosity of sirup in a batch vacuum crystallizer comprises an agitator including a rod which extends through a diaphragm overlying an opening in the crystallizer wall and is reciprocated, oscillated or wobbled by a drive combined with a detector which measures the force necessary to impart to the agitator a recurrent movement. The detector indicates the force on a viscosity scale and simultaneously actuates a device which records a viscosity curve. The viscosimeter forms part of an automatic control system which regulates the operation of the crystallizer.

16 Claims, 9 Drawing Figures l s I 20 /8 20/0 l6 l7 /6 L /3 PATENTED M25 272 SHEET 2 BF 6 FIG. 2

INVENTOPS HENRY THIELE, TILU VON DURING,

BERI] WEBNER BY W /QP/ their ATTOPNE Y memzmzsm 3636753 SHEET30F6 COMPRESSED GAS INVENTORS HENRY THIELE, TILU VON DURING.

GERIJ WEBNER 4 l4/w/ Zhiheir A TTOPNEY PATENTED m2 5 I972 SHEET 5 [IF 6 .4 in H mv Q40 (OE THEN .N v a m NYVW WT A Ma a in w. #76 r PATENTED M825 0972 SHEEY 5 OF 6 FIG. 7

IN VE N TOPS SUCTION GE NE RA 70/? SOURCE OF U N n n IR "0 n .Y N Wmm r... O ,W /T PT HM WA H .r VI

h m B 1 H PATENTED JANZSIQTZ SHEEI 8 OF 6 time [min] FIG. 5

TIME-LAG RELAY]! [kg/cm Viscosity expressed in pneumatic pressure INVENTOPS HENRV THIELE, m0 VUN niinms GERI] WEGNER their A TTORNEV AGITATOR AND VISCOSIMETER FOR SUGAR SIRUP OR THE LIKE AND APPARATUS UTILIZING THE SAME BACKGROUND OF THE INVENTION The present invention relates to improvements in agitators, particularly to agitators which can be utilized to stir the contents of vessels which are maintained at below or above atmospheric pressure. The invention also relates to a viscosimeter which can employ the improved agitator and to an apparatus which can employ the viscosimeter. The invention is especially suited for application in sugar factories, particularly for controlling the treatment of sirup in batch vacuum crystallizers.

SUMMARY OF THE INVENTION It is an object of our invention to provide a novel and improved agitator which is constructed and assembled in such a way that it can stir the contents of a vessel, for example, the contents of a batch vacuum crystallizer, without permitting uncontrolled escape or admission of fluids during stirring.

Another object of the invention is to provide an agitator whose operation is not affected by sudden and substantial changes in temperature, pressure, level, circulation and/or other characteristics of liquids which are being agitated.

A further object of the invention is to provide an agitator which can be readily combined with or installed on existing crystallizers or other types of vessels.

An additional object of the invention is to provide an agitator which can be used with advantage as a component part of a novel viscosimeter for use in sugar factories or for other purposes.

Still another object of the invention is to provide a viscosimeter which embodies the improved agitator and which is capable of furnishing continuous readings or signals to indicate changes in viscosity of sugar syrup or other liquids.

A concomitant object of the invention is to provide an arrangement for automatic regulation of crystallization in a batch vacuum crystallizer and to provide such arrangement with the improved agitator and viscosimeter.

Another object of the invention is to provide a novel method of regulating the crystallization of white, A-, B- and/or low-grade syrups in sugar factories by resorting to the aboveoutlined arrangement.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved arrangement itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partly elevational and partly sectional view of an agitator which embodies one form of our invention;

FIG. 2 is a fragmentary sectional view of a second agitator;

FIG. 3 is a fragmentary sectional view of a third agitator;

FIG. 4 is a diagrammatic perspective view of a viscosimeter which embodies the agitator of FIG. 1;

FIG. 4a is a fragmentary perspective view of a second viscosimeter which embodies an agitator similar to the one shown in FIG. 2; 7

FIG. 4b is an enlarged perspective view of a detail in the viscosimeter of FIG. 4a; 1

FIG. 5 is a diagrammatic view of a control arrangement for a batch vacuum crystallizer in a sugar factory, the control arrangement including a viscosimeter of the type shown in FIG.

FIG. 6 is a diagram showing the changes in viscosity of sirup in the crystallizer of FIG. 5; and

FIG. 7 is a schematic view of a battery of parallel connected crystallizers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an agitator which is utilized to stir the contents of a vessel 1. The latter comprises a sidewall which is provided with an opening 2 permitting the passage of an agitating member in the form of a rod 3. At least a portion of the opening 2 extends below the normal liquid level in the vessel 1. A nipple 4 extends into the opening 2 and is in sealing engagement with the wall of the vessel 1. The flange 4a of the nipple 4 constitutes an annular clamping member and engages that (inner) side of a flexible diaphragm 6 which faces the opening 2. The other side of the diaphragm is engaged by a second annular clamping member 12 which is fastened to the flange 40 by screws or bolts 5. The rod 3 extends through the central portion of the diaphragm 6 and is provided with a sealing member or bead 7 which is welded thereto and bears against the inner side of the diaphragm. The central portion of the diaphragm 6 is biased against the bead 7 by a sleevelike second sealing member 8 which surrounds the rod 3 and is biased against the diaphragm by a washer 10 which is slipped onto the threaded outer end 9 of the rod 3. The threaded outer end 9 takes two locknuts 11. The clamping members 4a, 12 engage the marginal portion of the diaphragm 6. The member 12 also serves as a closure for one end of a tubular bearing or housing 13 which has a flange l4 fastened to the member 12 by bolts or screws 15. The housing 13 accommodates two antifriction bearings 16 for a rotary output member 17 which is driven by an electric motor or by an analogous prime mover to be described in connection with FIG. 4. The output member 17 has a bore 18 whose axis intersects the axis of rotation of the output member 17 in a point 19 located in the central plane of the diaphragm 6. The bore 18 accommodates antifriction bearings 20 for the aforementioned sealing member 8. The bearings 20 are held apart by distancing sleeves 21, 22 which are fixedly held in the bore 18 by screws 23. The inner end portion of the rod 3 carries a hollow cylindrical agitating element 24 which is accommodated in the interior of the tank 1.

In the apparatus of FIG. 1, the rod 3 performs a wobbling or swiveling movement so that its left-hand portion (between the point 19 and the left-hand end) travels along the periphery of an imaginary cone whose apex is located in the point 19. Such wobbling or swiveling movement of the rod 3 is desirable when the forces necessary to maintain the rod in motion should remain substantially unchanged during a complete cycle, i.e., during each full revolution of the output member 17.

FIG. 2 illustrates a portion of a second agitator wherein the agitating member or rod 3a, whose left-hand end carries one or more agitating elements in the interior of the tank, is arranged to oscillate (i.e., to pivot back and forth) in a horizontal plane. To this end, the rod 3a is sealingly secured to a diaphragm 60, as by sealing members 7a, 7b, and its outer end portion extends through a horizontal slot 26 provided in a stationary guide 25. The drive means for oscillating the rod 3a comprises a resilient element here shown as a helical spring 27 which biases the right-hand end portion of the rod 3a downwardly, as viewed in FIG. 2, and a hydraulic or pneumatic cylinder 28 whose piston rod 29 can move the righthand end portion of the rod 3a upwardly, as viewed in FIG. 2. It is equally possible to provide the right-hand end of the rod 3a with a follower which extends into the groove of a cam (not shown) so that the rod 3a is caused to oscillate back and forth in response to angular or other displacement of the cam. The rod 3a is fulcrumed in the center of the diaphragm 6a.

Animportant advantage of the apparatus shown in FIG. 2 is that the magnitude of forces which the drive means must transmit to the rod 3a in order to impart to the latter an oscillatory movement is not dependent on the weight of the rod 3a and/or the weight of the agitating element or elements at the left-hand end of the rod.

In the apparatus of FIG. 2, the plane in which the rod 3a oscillates is parallel to the surface of liquid in the tank. This insures that variations in pressure and/or flow of liquid in the tank are least likely to influence the forces which are required to maintain the rod in motion. The magnitude of forces which are needed to impart to the rod 3:: an oscillatory movement varies sinusoidally.

FIG. 3 illustrates a portion of a third agitator wherein the diaphragm 6b forms part of a wall in the vessel and wherein the median portion of this diaphragm can be deformed by a reciprocable rod-shaped agitating member or plunger 3b which is connected to a drive means by a coupling member 30 and is reciprocable in a bearing 31. The drive means comprises a double-acting hydraulic or pneumatic cylinder 32 whose piston rod 33 is secured to the rod 3b by the aforementioned coupling member 30.

It is equally within the purview of our invention to construct the drive means for the agitating member 3, 3a or 3b in such a way that the agitating member performs a composite movement, for example, so that the agitating element 24 of FIG. 1 travels along an elipitical or eight-shaped path. Also, it might be desirable in some instances to mount the agitating member 3a of FIG. 2 in such a way that it oscillates in a vertical plane or in another plane which is inclined with reference to a horizontal plane.

As a rule, the agitator of FIG. 3 requires a diaphragm 6b which is larger than the diaphragm 6 or 60. Here, too, the magnitude of forces necessary to reciprocate the agitating member 3b varies sinusoidally. In accordance with a further modification which will be readily understood with reference to FIGS. 1 to 3, the member which carries one or more agitating elements can be caused to perform a composite movement which includes the swiveling or wobbling movement of FIG. 1, the oscillatory movement of FIG. 2 and. the reciprocatory movement of FIG. 3. This renders it possible to maintain the forces required to impart to the agitating member periodically recurrent movements at a constant magnitude during each stage of a movement. For example, and if the agitating member 3a of FIG. 2 is to perform a reciprocatory movement in addition to the oscillatory movement transmitted thereto by spring 27 and piston rod 29, the agitating member can also be caused to perform a wobbling movement to move the agitating element or elements along an elliptical or kidney-shaped path and to thus insure that the force required to move the agitating member remains constant at all stages of a cycle as shown in FIG. 3 by phantom lines, the agitating member 3b can extend through the diaphragm 6b and can carry one or more agitating elements in the interior of the vessel.

The agitating element 24 can be replaced by other types of agitating elements or it can be used in combination with one or more additional agitating elements. In the agitator of FIG. 1, the hollow cylindrical agitating element 24 can be replaced by a sphere 260 or the like (indicated by a phantomlike circle), and such sphere or the element 24 can be provided with extensions or projections 26b in the form of lobes or ribs having the same or different length, profile and/or spacing. By employing an agitating element which is not of spherical, cylindrical or other symmetrical form, the designer of the apparatus can influence the magnitude of forces which are required to maintain the agitating member in motion. For example, an oddly shaped agitating element can be used when the agitating member is caused to perform a composite movement including as oscillatory, a wobbling and a reciprocatory movement. It is also possible, particularly in. the agitator of FIG. 2, to employ one or more fin-shaped agitating elements 24c extending preferably at right angles to the plane of oscillatory movement of the member 3a. The agitator of FIG. 2 can also employ a series of axially spaced disk-shaped agitating elements 24d which may but need not be provided with protuberances or other unevennesses. The disk-shaped agitating elements can be provided with projections 24 and/or 24f which extend from their peripheral surfaces and/or from their end faces and such projections may be bounded by flat, spherical, cylindrical or otherwise configurated surfaces. Furthermore, each such projection may be provided with protuberances in the form of cams, lobes, fins 26g, ribs or the like.

The agitator of FIG. 3 can be used in apparatus wherein the vessel 1 should be provided with smooth internal surfaces and wherein the agitator serves exclusively as a means for determining the viscosity of the contents of the vessel. Such vessels are often employed in viscose spinning apparatus for cellulose viscose. Any recesses, openings or like unevennesses in the walls of a viscose spinning tank might produce dead corners for deposition of viscose whereby the material sets, undergoes changes, coagulates and is otherwise affected to cause clogging of filters and spinnerets. In such tanks, a portion of a wall or a portion of a conduit which communicates with the tank, can be formed by a diaphragm which is yieldable and expansible and whose outer side is acted upon by the rod 3b or another reciprocable plunger. The force required to reciprocate the plunger is indicative of viscosity. In other words, the agitator can be used exclusively-as a stirring means, exclusively as a component of a viscosimeter, or both. The innate elasticity of the diaphragm 6b then serves to return it to unstressed position when the plunger 3 b performs a return stoke, i.e., the diaphragm 6b then acts not unlike a spring. If the innate elasticity of the diaphragm 6b is insufficient to effect rapid return movement to unstressed position, the head of the plunger 3b can be connected to the diaphragm by vulcanizing, by mechanical coupling means or in another way so that the plunger cooperates with the diaphragm in a manner as known from the art of diaphragm valves.

The agitator of FIGS. 1 to 3 is particularly suited for use in connection with vessels whose contents are maintained at superatmospheric pressure or at below-atmospheric pressure. However, the agitator can also be used in connection with open or closed vessels wherein the contents are maintained at atmospheric pressure. One of several important advantages of this agitator is that the agitating member 3, 3a or 3b need not rotate in order to bring about stirring of the contents of the vessel by way of the agitating element or elements. This is in contrast to the operation of conventional agitators wherein the agitating member is a shaft which is rotated about its axis and carries blades, vanes, propellers or analogous agitating elements which must extend into the contents of the vessel. In order to prevent uncontrolled escape of liquid contents from the vessel, especially if such contents are maintained at an elevated pressure, the rotary shaft of a conventional agitator must extend through a stuffing box which is mounted in the wall of the vessel. Since the shaft rotates in the stuffing box, friction invariably produces wear which must be compensated for by periodic adjustments of the stuffing box. If the operator fails to detect such wear, he is likely to adjust the stuffing box upon detection of actual leakage which can cause losses in valuable material and contamination of the surrounding area. As a rule, the operator will attempt to adjust the stuffing box in such a way that it will thereupon provide a satisfactory seal for extended periods of time, i.e., the stuffing box is then too tight and causes additional wear.

Since the agitating members of the agitators shown in FIGS. 1 to 3 need not rotate in or reciprocate through the diaphragm 6, they need not be surrounded by stuffing boxes so that periodic adjustments which are necessary in aforedescribed conventional agitators can be dispensed with. This reduces the wear and prevents escape of the contents of the vessel or penetration of air or other foreign matter into the interior of the vessel.

The agitator of FIGS. l-to 3 is particularly suited for use in viscosimeters which are employed to determine the viscosity of liquids in the manufacture of sugar. As is well known, crystallization of sugar is often carried our in vacuum crystallizers wherein a mixture of liquid and crystals undergoes controlled crystallization while a feed delivers variable amounts of syrup. The process is a batch process and the crystallization depends on a number of factors, for example, on evaporation of water which, in turn, depends on the rate of circulation of solution in the vessel. The circulation is assisted by an agitator of the aforedescribed conventional type wherein a rotary shaft carries blades or vanes and must rotate in a stuffing box. The

drawbacks of stuffing boxes were outlined hereinbefore. Moreover, the entire boiling process is regulated in dependency on the viscosity of syrup because such viscosity is indicative of the progress of crystallization. The viscosity can be determined by measuring the consumption of energy which is required for agitation of the contents, i.e., by determining the changes in energy consumption. Such energy consumption is influenced by friction between a rotating shaft and the stuffing box, i.e., the friction decreases when the material of the stuffing box wears away but increases suddenly to a multiple of the minimum friction when the stuffing box is adjusted. Immediately after adjustment of the stuffing box, that percentage of energy which is used to overcome friction between the rotating shaft and the stuffing box is much higher than when the seal between the shaft and the stuffing box is rather loose. Furthermore, and if the revolving shaft enters the vessel at a level above the liquid surface, splashes of liquid can reach the stuffing box and affect the rotation of the shaft by forming an adhesive film which hinders rotation of the shaft with reference to the stuffing box. This also contributes to false readings in measurement of energy consumption. Finally, the vessel is cleaned or rinsed with saturated steam at a pressure of 0. I0.2 kg./cm. above atmospheric pressure. The condensate penetrates into the clearance between the shaft and the stuffing box and often causes corrosion which results in increased friction. Analogously, and when the shaft extends into the vessel below the liquid level, atmospheric air can penetrate into the liquid when the vessel is maintained under vacuum. Bubbles of air in the syrup reduce the resistance to agitation so that the measurement of energy required for agitation furnishes false readings of viscosity.

When the agitator of FIG. 1, 2 or 3 is used in such crystallizers, the above-outlined drawbacks are eliminated in a very simple way so that the measurement of viscosity is more reliable.

A viscosimeter which employs the agitator of FIG. 1 is illustrated in FIG. 4. The output member 17 causes wobbling movements of the agitating member 3 in a manner as shown in FIG. 1. This output member 17 is connected with a sprocket wheel 17a which is driven by an endless chain 35. The latter is trained over a driver sprocket wheel 36 which is driven by an output shaft 37 receiving torque from the rotor of an electric gear motor 38 through the intermediary of a stepdown transmission 39. The length of the chain 35 is selected in such a way that its stretches sag, and its upper stretch 35a is engaged by a rotary detector 40 which is mounted between two prongs 41 on the left-hand arm of a two-armed lever or indicator 42 which is fulcrumed at 43 and whose right-hand arm carries a longitudinally adjustable counterweight 44. The left-hand arm of the lever 42 is formed with an index 45 which travels along a graduated scale 46 which is calibrated to" indicate the viscosity of liquid which is being stirred by the element 24 on the agitating member 3.

The diameters of the sprocket wheels 17a, 36 are identical. The shaft 37 of the transmission 39 drives the sprocket wheel 36 at rpm. As explained in connection with FIG. I, the agitating member 3 and the output member 17 are mounted on the wall of the vessel 1. The motor 38, transmission 39,

shaft 37 and sprocket wheel 36 can also be mounted on vessel 1. The detector 40 is preferably a sprocket wheel which meshes with the stretch 35a and rotates with reference to the prongs 41 when the chain 35 is in motion. The position of the counterweight 44 determines the pressure with which the detector 40 bears against the upper stretch 35a. By changing the position of the counterweight 44, the operator can change the range of viscosities which are to be measured by the structure of FIG. 4. Also, the counterweight can serve as a means for accurately calibrating the viscosimeter.

An air-discharging nozzle 47 is disposed at a level above the left-hand arm of the lever 42 and is adjustable up and down. This nozzle receives compressed gas through a branch conduit 48 which communicates with a main supply conduit 49. The mainsupply conduit 49 is connected to a conventional pneumatically operated recorder 50 and contains a regulating valve 51. In the illustrated embodiment, the diameters of the sprocket wheels 17a, 36 are about 100 mm. each, and the maximum slack of the upper stretch 35a of the chain 35 is 70 The parts 40-51 together constitute an indicator means which indicates the changes in viscosity of liquid in the vessel as a function of changes in the slack of the stretch 35a.

The operation is as follows:

The motor 38 drives the sprocket wheel 36 at 20 rpm. whereby the chain 35 drives the output member I7 which causes the agitating member 3 to perform wobbling movements as described in connection with FIG. 1. If the viscosity of the medium into which the agitating element 24 extends is low, e.g., if such medium is water, the weight of the left-hand arm of the lever 42, the weight of the prongs 41 and the weight of the detector 40 bear on the upper stretch 35a and cause this stretch to maintain its central portion at the lowermost level. This results in stretching or straightening of the lower stretch 35b. If the agitating element 24 extends into a medium of higher viscosity, such medium offers a greater resistance to wobbling movement of the agitating member 3 and the weight of the detector 40 does not suffice to maintain the lower stretch 35b in fully extended position. In other words, the slack in the upper stretch 35a decreases and the detector 40 moves upwardly. If the viscosity of the liquid is very high (e.g., if the medium in which the agitating element 24 wobbles is a mixture of sugar and molasses), the upper stretch 35a is free of slack and the slack of the lower stretch increases to a maximum value. The magnitude of viscosity can be read on the scale 46, i.e., the inclination of the lever 42 is indicative of viscosity.

The purpose of the nozzle 47 is to facilitate continuous recordal of viscosities by the recorder 50. This nozzle detects the position of the lever 42. The conduit 49 delivers air at a pressure of 1.2 atmospheres and the positioning of the noule 47 is such that its orifice or orifices are sealed by the lever 42 when the follower 40 assumes an uppermost position which is indicative of a predetermined maximum viscosity. All of the air which is admitted via conduit 49 then reaches the valve 51 and recorder 50. When the viscosity decreases, the noule 47 begins to discharge increasing amounts of air and the stylus of the recorder 50 records the corresponding viscosity on a drum or another suitable travelling carrier.

It is clear the viscosimeter of FIG. 4 can be modified in a number of ways without departing from the spirit of the invention. Thus, the drive for the agitating member 3 can be altered by using a belt as a substitute for the chain 35, by employing a pneumatic or hydraulic prime mover, by maintaining the detector 40 in engagement with the lower stringer 35b of the chain 35 under the action of a spring, or by utilizing the lever 42 as a stylus for recordal of viscosities on a travelling carrier. Moreover, the lever 42 can be replaced by a linkage, by a gear train or by any other suitable means which can furnish visual indications and/or permanent recordals of viscosities.

The viscosimeter of FIG. 4 is particularly suited for use in connection with highly viscous substances, especially for continuous determination of viscosity of substances which are enclosed in a vessel at subatmospheric or superatmospheric pressure. As stated before, the viscosimeter can be used for determination of viscosity of mixtures of sugar with molasses or analogous mixtures with a maximum viscosity of up to 150,000 cp.

In heretofore known viscosimeters, the agitating element or elements are mounted on a revolving shaft which is driven by a motor or the like. The resistance which the viscous substance offers to rotation of the agitating element or elements is determined and is indicative of viscosity. A drawback of presently known instruments which are utilized to determine the resistance to rotation of the agitating elements is that they are overly sensitive and therefore are not suited for extended use in connection with the manufacture of sugar, i.e., in connection with determination of viscosity of tough media, such as in 'ing of rubber or the like. The drive for causing the agitating element 24 to perform a pendulum (oscillatory) movement in a horizontal plane comprises a connecting rod 290 one end of which is coupled to the rear end of the agitating member 3a by a universal joint 29b and the other end of which is tiltably mounted on an eccentric pin 290 provided on a sprocket wheel 17a. A second universal joint is preferably installed between the pin 29c and the connecting rod 29a. The manner in which the sprocket wheel 17a is driven by the chain 35 and sprocket wheel 36 when the motor 38 is on is the same as shown in FIG. 4.

A substantially U-shaped guide 25a confines the agitating member 3a and agitating element 24 to the pendulum movement in a horizontal plane. This guide 25a has two flanges which are free to rotate back and forth about coaxial vertical stubs 25b, 25c which are located in the central plane of the diaphragm 6a. The web of the guide 25a is connected to the agitating member 3a.

The viscosimeter of FIG. 4 or FIGS. 4a-4b can be utilized in the manufacturing of sugar in a manner to be described in connection with FIGS. 5-7. Its purpose is to insure fully automatic regulation of crystallization in dependency on the viscosity of syrup in the crystallizer vessel. The improved viscosimeter is sufficiently rugged to stand long periods of use in a sugar-manufacturing plant.

FIG. 5 illustrates a source or pan 102 which contains fresh syrup and can supply syrup to a batch vacuum crystallizer vessel 101. The admission of syrup from the pan 102 into the vessel 101 takes place on closing of a switch K1 which actuates a valve 103 in a feed conduit connecting the pan with the vessel. A float 105 in the pan 102 descends on opening of the valve 103 and ultimately actuates a switch K2 to close the valve 105 and to thus interrupt the feed of syrup into the vessel 101. The feed of syrup to the vessel 101 is indicated in the diagram of FIG. 6 by the straight line between the points A and B.

In the next step, the syrup is thickened (curve B-C in FIG. 6) by expulsion of water in response to admission of steam. The viscosity of syrup rises to a predetermined value (point C in the diagram of FIG. 6) at which the inoculation begins. The admission of steam into the vessel 101 is started in response to closing of the aforementioned switch K2 which opens a steam valve 104 in a steam supply conduit. At such time, a valve 106 permits evacuation of air from the vessel 101 by means of a fan or another suitable suction generating device.

Inoculation of thickened syrup in the vessellQl takes place in response to admission of an inoculating suspension for a predetermined interval of time. It is initiated when the viscosity of syrup reaches the predetermined value (point C in FIG. 6) which is measured by a viscosimeter 107, preferably of the type disclosed in FIG. 4. The viscosimeter 107- then closes a switch K3 which opens an electromagnetic valve 110 in the discharge line 111 of a small container 109 which is provided with an agitator 108. The container 109 then furnishes an inoculating suspension by way of the line 111. The valve 110 closes automatically after a predetermined interval of time in response to deenergization of a time-lag relay (1 in FIG. 6) which is energized on closing of the switch K3. The agitator 108 may but need not be of the type shown in FIG. 1, 2 or 3.

The formation of nuclei takes place during the interval while the viscosity of liquid in the vessel 101 rises from C to D on the curve of FIG. 6. In order to insure uniform distribution of nuclei which are admitted from the container 109 into the syrup which is contained in the vessel 10]. the contents of the vessel are boiled for a short period of time without addition of viscosimeter 107 closes a switch K4 which starts two regulators 112, ll 3 serving to terminate the formation of nuclei in the vessel 101.

In the next step, the viscosity of the contents of the vessel 101 is reduced to a value VK (FIG. 6) in response to admission of fresh syrup and condensate. The admission of condensate is interrupted and the viscosity is reduced still further (to VS) in response to continued admission of fresh syrup. The viscosity VK is thereupon maintained by boiling and continued admission of fresh syrup until the vessel 101 is halffilled.

The admission of condensate and fresh syrup into the vessel 101 (between the points D-E of the viscosity curve shown in FIG. 6) is controlled by the aforementioned regulators 112, 113. The regulator 112 controls the admission of condensate and the regulator 113 controls the admission of fresh syrup.

The regulators 112, 113 are energized simultaneously when the viscosity rises to D and the regulator 112 then opens a valve 1 14 which connects the vessel 101 with a container 1 16 for condensate. The regulator 113 opens a valve 115 which connects the vessel 101 with a main source 117 of fresh syrup. When the viscosity of the contents of the vessel 101 decreases to VK, the regulator 112 is deenergized to close the valve 114 and to maintain the valve 114 in closed position as long as the viscosity remains below VK. In other words, no additional condensate enters the vessel 10] if the viscosity of syrup therein does not rise above VK. The regulator 113 remains energized and controls the viscosity of the contents of the vessel 101 so that such viscosity decreases to VS and remains at or close to such value. This is achieved by opening the valve 11 5 whenever the viscosity rises above VS in response to continued boiling- The valve 115 closes gradually when the viscosity decreases toward the value VS and remains closed when the viscosity decreases below VS. Signals indicating the desired rated values of VK and VS are furnished to the regulators1'12, 113 by an integrator or multiplier 119 which in turn is controlled by a level detector 118. The latter furnishes pneumatic signals of rising intensity which indicate the rising level of the contents of the vessel 101 during boiling. Such signals are multiplied in the integrator 119 by a predetermined factor and. the resulting pneumatic output signals are transmitted to the regulators 112, 1 13.

It was found that crystallization should proceed initially at a relatively low viscosity which should remain constant during a predetermined interval of time (between the graduations 30 and 50 on the ordinate of FIG. 6). In the next stage. the viscosity should rise together with a rise in the level of the contents of the vessel 101. This is achieved in the aforedescribed manner as represented by the portion of the curve between the points D-E in FIG. 6.

The integrator 119 produces pneumatic output signals in response to input signals received from the level detector 118. The intensity of such input signals increases more or less gradually; however, the integrator 119 is programmed in such a way that it initially produces an output signal of constant magnitude and that it thereupon furnishes an output signal whose intensity increases proportionally with intensity of input signals. The regulators 112, 113 receive additional signals from the viscosimeter 107 as a function of changing viscosity in the vessel 101. All disturbances which are caused by fluctuations in vacuum, steam pressure, temperature and/or other factors which influence the boiling process and the viscosity are compensated for by the regulators 112, 113 in such a way that the valve 115 closes more or less when the viscosity decreases below the desired optimum value VS (for example, due to decreasing vacuum, rising temperature or rising steam pressure in the vessel 10! When the viscosity rises above VS, for example, in response to increasing vacuum, decreasing temperature, and/or decreasing steam pressure in the vessel 101, the valve 115 opens to such an extent that the inflowing thin syrup causes a reduction in the viscosity of the mass in the vessel 101. ln the event of unexpectedly large disturbances which tend to cause a sudden rise in viscosity, the 1 regulator 112 is actuated and assists the regulator 113 to reduce the viscosity to a desired value. As stated before, the

regulator 112 responds when the viscosity rises above the value VK. Thus, this regular is active in emergency situations to prevent excessive evaporation of water and resulting higher consumption of energy.

During boiling, the vessel receives (for an interval of about 50 minutes) such quantities of syrup that it is practically filled with liquid. When the filling of the vessel is completed, its contents close a switch K5 which is connected with and causes inactivation of the regulators 112, 113, i.e., closing of the valves 1 i4, 115.

In the next stage, the contents of the vessel 101 are boiled while the valves 114, 5 remain closed so that the viscosity rises to a value P which corresponds to a solids content of 90-95 percent. When the viscosity reaches such value, the viscosimeter 107 closes a switch K6 which energizes time-lag relays (not shown) sewing to shutoff the valves 104, 106 and to open a ventilating valve, a dump valve 125 (FIG. 7) and a steam-evacuating valve 126 (FIG. 7). This completes the boiling operation.

An optional step is indicated by the position of the viscosity curve between the points E-E' in FIG. 6. It can happen that the boiling of the contents of the vessel 101 (while the regulators 112, 113 are deenergized) cannot begin immediately after the viscosity reaches the value E. For example, it can occur from time to time that the treatment at the next-following stations is not completed in time so that the boiling operation must take longer. In other words, the syrup is boiled, when necessary, to maintain the viscosity at the valve VK, but without further growing of crystals. This is achieved by manually deenergizing the regulator 113 and by causing further operation of the regulatorl 12. Alternatively, the regulator 112 can be energized by manipulating the switch K6 subsequent to automatic deenergization of both regulators by the switch K5. Thus, the operator then causes the valve 114 to admit such quantities of condensate as are expelled from the syrup in response to continued boiling in the vessel 101. This operation is terminated by hand at E so that the boiling of syrup while the valves 114, 115 are closed can begin (from E to F).

FIG. 7 shows an aggregate with a battery of three parallelconnected vessels 101.

It will be seen that the apparatus of FIG. 5 comprises the following essential components:

I. A pan 102 which is controlled by the float 105 to discharge into the vessel 10! a predetermined quantity of fresh syrup whereby the float initiates the admission of steam by way of the switch K2 and valve 104;

2. A viscosimeter 107 which determines the viscosity of the contents of the vessel 101 and which controls a. The valve 110 for admission of predetermined quantities of inoculating suspension from the source 109 when the viscosity rises to a predetermined value,

. The regulators 112, 113 to control the viscosity so that the viscosity remains within a predetermined range during admission of fresh syrup, such regulations being modified by signals from the level detector 113 and integrator 119,

c. The closing of valve 104 and opening of valve 106 (and other valves) when the viscosity rises to a value corresponding to 90-95 percent of solids content; and

3. The switch K5 which deenergizes the regulators 11 2, 113 to close the valves 114, 115. V

In accordance with the presently prevailing practice, boiling of syrup in batch crystal evaporators of sugar factories is controlled by hand in accordance with a complicated program.

The operator must observe readings furnished by various pressure gauges, vacuum gauges, thermometers, conductivity detectors and other instruments and he must evaluate such readings for proper regulation of boiling. The operator must rely on his experience to properly calculate the momentary viscosity at various stages of treatment in the evaporator.

It was already proposed to simplify the regulation of boiling by automatic determination of viscosity on the basis of conductivity of the contents of the evaporator, i.e., to automatically regulate the crystal formation as a function of changes in conductivity. A drawback of such procedure is that the percentage of dissociated salts which determine the conductivity fluctuates within a rather wide range.

The crystallization is preferably carried out in vacuo in order to avoid discoloration of the sugar-syrup mixture at elevated temperatures. Such discoloration is the result of caramelization. The operation in vacuo insures that the boiling point of the sugar-syrup mixture remains at a very low level. It is also desirable to maintain the pressure of steam, which is needed for boiling of the tiller, at a relatively high and constant value. This reduces the time necessary for boiling. However, and since a sugar factory normally employs a large number of evaporators for a variety of products, and since it is preferred to supply steam to all of the evaporators from a common source as well as to connect all evaporators to a common suction-generating unit, this often causes considerable fluctuations in the delivery of steam and/or in subatmospheric pressure for a variety of reasons. For example, an outlet for sugar crystals might not close tightly in response to deposition of crystals on the dump valve. This permits uncontrolled entry of air and reduces the vacuum in the respective evaporator. Such reduction in vacuum is communicated to other evaporators since all of the evaporators are normally connected to a common suction-generating unit. It can also happen that the condensate collecting unit cannot evacuate the condensate at a desired rate. A rise in the amount of condensate affects the delivery of fresh steam to the particular evaporator. Since the thus affected evaporator receives lesser quantities of steam, the remaining evaporators receive more steam than necessary. Thus, the boiling of syrup in the directly affected evaporator is insufficient but is excessive in the other evaporators. When a battery of 10 or 12 evaporators receives steam from a common source and is connected to a single suction generator, improper operation of one or a few evaporators can exert a very pronounced undesirable influence on the remaining evaporators so that it is practically impossible to establish and sustain in each evaporator optimum conditions for development and growing of sugar crystals, i.e., to maintain the viscosity within an optimum narrow range. This is due to the absence of control systems which are capable of automatically regulating the viscosity in batch vacuum crystallizers. The apparatus of FIG. 5 is equipped with a novel control system which is particularly suited to regulate the formation of crystals in white-, A-, B- and low-grade fillers in a novel and reliable way.

The method which has been described in connection with FIGS. 5 and 6 comprises the following important steps:

1. Admission of a predetermined amount of fresh syrup from the pan 102 into the vessel 10 is automatically completed by the floatl 05 response to evacuation of the pan 102.

2. Completion of admission of fresh syrup into the vessel 101 triggers the admission of steam via valve 104 while the and fresh syrup (regulators 112, ll 3) and thereupon by admission of fresh syrup (regulator l 13).

6. Terminating the admission of fresh syrup when the level of liquid in the vessel rises to a desired value.

7. Boiling the contents of the vessel until the viscosity rises to a desired maximum value.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Let ters Patent is set forth in the appended:

1. In an arrangement of the character indicated, particularly in a sugar factory,a combination comprising a vessel arranged to contain liquids of variable viscosity extending above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane, said drive comprising a rotary output member operatively connected with said agitating member and an endless flexible element for rotating said output member; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, suchforces being proportional to the viscosity of liquid in said vessel and said flexible element having a portion whose slack changes as a function of changes in the magnitude of said forces, said measuring means comprising indicator means for indicating the changes in viscosity of liquid in said vessel as a function of changes in said slack.

2. A combination as defined in claim 1, wherein said indicator means comprises movable detector means which tracks said portion of said flexible element.

3. A combination as defined in claim 2, wherein said detector means bears by gravity on said portion of said flexible element.

4. A combination as defined in claim 2, further comprising means for biasing said detector means against said portion of said flexible element.

5. A combination as defined in claim 1, wherein said drive further comprises a rotary member connected with said output member, said flexible element being trained around said rotary member.

6. A combination as defined in claim 1, wherein said drive further comprises a rotary member and a prime mover having a rotary output member connected with said rotary member, said flexible element being trained around said rotary member.

7. A combination as defined in claim 6, wherein said flexible element is a chain and said rotary member is a sprocket wheel, said drive further comprising a second sprocket wheel provided on said first-mentioned output member, said chainbeing trained around said second sprocket wheel and said sprocket wheels having identical diameters.

8. A combination as defined in claim 1, wherein said flexible element is a chain and said indicator means comprises a twoarmed lever pivotable about a fixed axis and a sprocket wheel rotatably mounted on one arm of said lever and tracking said portion of said chain, the angular position of said lever being indicative of viscosity of the liquid in said vessel.

9. A combination as defined in claim 8, wherein said indicator means further comprises a nozzle arranged to discharge a compressed gas and positioned adjacent to said lever so that 10. A combination as defined in claim 9, wherein said indicator means further comprises a sourceof compressed gas having supply conduit means connected with said nozzle, said means responsive to changes in the rate of gas discharge from said nozzle comprising pneumatic recorder means connected with said conduit means.

11. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an, elongated agitating member extending into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel and a rod having an intermediate portion which extends through the central portion of said diaphragm and having the agitating element mounted thereon; means for holding said agitating member in substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.

12. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one substantially diskshaped agitatihg element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.

13. in an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extend above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising a rod and at least one agitating element located in said vessel and mounted on said rod, said agitating element being of circular outline and being coaxial with said rod; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.

14. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel, said agitating element being provided with a plurality of protuberances which stir the contents of said vessel in response to movement of said agitating member; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.

15. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel aragitating member in said plane, said drive comprising means for imparting to said agitating member recurrent movements with a force which is at least nearly constant at each stage of the respective movement; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.

16. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening and at least a portion of the supply of liquid in said vessel being selected from the group consisting of sugar syrup and a mixture of sugar syrup with sugar crystals; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said ves sel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel. 

1. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain liquids of variable viscosity extending above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane, said drive comprising a rotary output member operatively connected with said agitating member and an endless flexible element for rotating said output member; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel and said flexible element having a portion whose slack changes as a function of changes in the magnitude of said forces, said measuring means comprising indicator means for indicating the changes in viscosity of liquid in said vessel as a function of changes in said slack.
 2. A combination as defined in claim 1, wherein said indicator means comprises movable detector means which tracks said portion of said flexible element.
 3. A combination as defined in claim 2, wherein said detector means bears by gravity on said portion of said flexible element.
 4. A combination as defined in claim 2, further comprising means for biasing said detector means against said portion of said flexible element.
 5. A combination as defined in claim 1, wherein said drive further comprises a rotary member connected with said output member, said flexible element being trained around said rotary member.
 6. A combination as defined in claim 1, wherein said drive further comprises a rotary member and a prime mover having a rotary output member connected with said rotary member, said flexible element being trained around said rotary member.
 7. A combination as defined in claim 6, wherein said flexible element is a chain and said rotary member is a sprocket wheel, said drive further comprising a second sprocket wheel provided on said first-mentioned output member, said chain being trained around said second sprocket wheel and said sprocket wheels having identical diameters.
 8. A combination as defined in claim 1, wherein said flexible element is a chain and said indicator means comprises a two-armed lever pivotable about a fixed axis and a sprocket wheel rotatably mounted on one arm of said lever and tracking said portion of said chain, the angular position of said lever being indicative of viscosity of the liquid in said vessel.
 9. A combination as defined in claim 8, wherein said indicator means further comprises a nozzle arranged to discharge a compressed gas and positioned adjacent to said lever so that the latter influences the rate of gas discharge in response to changes in the angular position thereof, and means responsive to changes in the rate of gas discharge from said nozzle to indicate such changes as a criterion of viscosity of the liquid in said vessel.
 10. A combination as defined in claim 9, wherein said indicator means further comprises a source of compressed gas having supply conduit means connected with said nozzle, said means responsive to changes in the rate of gas discharge from said nozzle comprising pneumatic recorder means connected with said conduit means.
 11. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel and a rod having an intermediate portion which extends through the central portion of said diaphragm and having the agitating element mounted thereon; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.
 12. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one substantially disk-shaped agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.
 13. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extend above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising a rod and at least one agitating element located in said vessel and mounted on said rod, said agitating element being of circular outline and being coaxial with said rod; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating membeR in said plane, such forces being proportional to the viscosity of liquid in said vessel.
 14. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel, said agitating element being provided with a plurality of protuberances which stir the contents of said vessel in response to movement of said agitating member; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.
 15. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane, said drive comprising means for imparting to said agitating member recurrent movements with a force which is at least nearly constant at each stage of the respective movement; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel.
 16. In an arrangement of the character indicated, particularly in a sugar factory, a combination comprising a vessel arranged to contain a supply of liquid which extends above a predetermined level, said vessel having wall means provided with an opening and at least a portion of the supply of liquid in said vessel being selected from the group consisting of sugar syrup and a mixture of sugar syrup with sugar crystals; a substantially vertically extending diaphragm connected with said wall means to seal said opening; an elongated agitating member extending through said diaphragm and into said vessel below said predetermined level, said agitating member being fulcrumed in said diaphragm and comprising at least one agitating element located in said vessel; means for holding said agitating member in a substantially horizontal plane against appreciable rotary and lengthwise movement; a drive for oscillating said agitating member in said plane; and measuring means for determining the magnitude of forces necessary to move said agitating member in said plane, such forces being proportional to the viscosity of liquid in said vessel. 